Diffusion

DiffusionDiffusion

IGCSE Science - BiologyIGCSE Science - Biology

I need some deodorant!I need some deodorant!

Close your eyes and as soon as you notice a change in our environment stand up.

I’m going to release something in the room.

Now you have 2 min as a group to explain what just happened!

Close your eyes and as soon as you notice a change in our environment stand up.

I’m going to release something in the room.

Now you have 2 min as a group to explain what just happened!

DiffusionDiffusionDiffusion is the movement of molecules down a

concentration gradient from an area of high

concentration to an area of low concentration,

until evenly spread out.

Why is diffusion important?

Why is diffusion important?

All living cells rely on diffusion to live.

They use it for:

getting raw materials for respiration (dissolved

substances and gases) removing waste products (eg. from respiration)

photosynthesis in plants (raw materials in, waste products out)

Examples…

Respiration- gas exchangeRespiration- gas exchange

SEM photos of lung alveoli

In breathing you exchange carbon dioxide (CO2) and oxygen (O2) between

alveoli in the lungs and the blood.

This is an example of diffusion.

Respiration- in cellsRespiration- in cellsfood + oxygen carbon dioxide + water + energy

Respiration & diffusionRespiration & diffusion

Photosynthesis & Diffusion

Photosynthesis & Diffusion

Carbon dioxide

diffuses in through

the stomata

Carbon dioxide

diffuses in through

the stomata

Oxygen and

water diffuse out

of the stomata

carbon dioxide + water oxygen + glucose

OsmosisOsmosisOsmosis is a special case of diffusion.It is the nett movement of water across a selectively or partially permeable membrane from a high concentration to a low concentration.

The cell membrane has very small holes in it. Small molecules can pass through, but larger ones can’t.

We say it is selectively permeable or semi-permeable or partially permeable.

Selectively permeable membrane ???

High Water Concentration,

few molecules of solute.

Dilute solution

Low Water Concentration, many

molecules of solute.

Concentrated solution

Water molecule Solute moleculeKey:

Water concentration gradientWater concentration gradient

Water movement

In osmosis water moves both ways to balance up the concentrations. The overall (nett) movement is to the area of low water concentration.

Osmosis in actionOsmosis in action

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

Have a look at:

Why is this not funny if you were a slug??

Why is this not funny if you were a slug??

Osmosis in CellsOsmosis in Cells

Some real time osmosis videos to set the mood!Some real time osmosis videos to set the mood!

Group Starter Activity

Mr and Mrs Kim went on holiday to Jeju for a few days.

When they came back their favourite plant looked like this!

Explain the changes in terms of water movement

5 days ago Today

Plants rely on the movement of water through them:

Root hairs take in water from the soil by osmosis.

Water always moves to areas of lower water concentration.

Why is osmosis important?Why is osmosis important?

We say that the cell is turgid.

Water moves into a plant cell.

The cell wall stops the cell from bursting.

Turgid cell.

Vacuole is filling all the space and pushing against cell wall

This is useful as it gives plant stems support

Plants- Water moving inPlants- Water moving in

Cell turgor pressureCell turgor pressure

If a lot of water leaves the cell, the cytoplasm starts to peel away from the cell wall and we say the cell has undergone plasmolysis.

When water moves out of the plant cell vacuole, by osmosis, it becomes flaccid

Flaccid cell.

Vacuole is much smaller and taking up less space

Plants- Water moving outPlants- Water moving out

Plasmolysis Plasmolysis

Osmosis in Plant CellsOsmosis in Plant CellsLow water

concentration outside the cell

(ie concentrated solution outside)

High water concentration outside the cell

(ie pure water or dilute solution outside)

Equal water concentrations inside & out

(ie equal solute concentrations inside & out)

Animal cells have no cell wall to stop the swelling, just a flexible cell membrane.

Animals- Water moving inAnimals- Water moving in

haemolysed turgid then burst

If an animal cells are put in pure water (HWC) they take in water by osmosis until they burst.

normal

haemolysed

Animals- Water moving outAnimals- Water moving outIf an animal cells are put in a concentrated solution (LWC) they lose water by osmosis until they become shrunken or haemolysed.

http://zoology.okstate.edu/zoo_lrc/biol1114/tutorials/Flash/Osmosis_Animation.htm

normal

1. What is a partially permeable membrane?

2. Which substance moves by osmosis?

3. What happens to plant cells that take up water by osmosis, and what do you call the cell?

4. What happens to plant cells that lose water by osmosis, and what do you call the cell?

5. What does ‘haemolysed’ mean? How does it happen?

Quick Quiz- OsmosisQuick Quiz- Osmosis

Water, H2O

A membrane that only lets small molecules through it

The cells become ‘full’ of water and are called turgid

The cytoplasm comes away from the cell wall and the cells are called plasmolysed.

Animals cells which have lost water become shrunken and are called haemolysed.

OsmosisTwo sugar solutions are separated by a semi-permeable membrane like Visking or dialysis tubing.

The larger sugar molecules are too big to pass through the membrane but the water particles can pass.

Dilute sugar solution Concentrated sugar solution

On both sides of the membrane particles move randomly hitting the membrane and each other.

OsmosisOsmosis is like diffusion except there is a membrane in the way.

If a water molecule on either side hits the membrane it will bounce off - if it hits a hole it will go through.

The sugar molecules can’t pass and just bounce off.


Water molecules from both sides pass through the membrane but there is a nett movement from left to right.

Nett movement is down the water gradient.

Osmosis

Osmosis is the diffusion of molecules from an area of high concentration to an area of lower concentration through a partially permeable membrane.


In terms of water potential we can say that osmosis allows the movement of water particles from areas of high water concentration or “potential” to areas of low water concentration or “potential”, across a semi-permeable membrane.

Nett movement is down the water gradient.

Now try your osmosis practicals

Now try your osmosis practicals

Documents

Diffusion